Of a bad reason or a bad effect?

Bad reasons are a dime a dozen. Maybe they just don't want to. They don't like the idea, and they're stubborn. Or they made a deal with one or two companies and don't want to allow others, even though some customer would really prefer the disallowed ones or can't get service from the allowed ones.

For bad effects, it means that the customer can't get the food they want, even with 100% knowledge that it's a third party picking it up, and that the quality will be imperfect in a way that's not the restaurant's fault.

Here, let me quote someone else from this same comment page: "Last night I wanted w bottle of alcohol for new years celebration. I already had a few drinks so I didn't want to drive. Unfortunately no delivery service had an agreement with any local liquor stores."

And, I mean, for non-food items imagine how bad it would be if you needed explicit permission from the manufacturer to sell something on ebay. Food's not that different.